Periodic inspections of a gas turbine engine require the disassembly and subsequent re-assembly of various heat-insulating duct work that surrounds various components of the gas turbine engine. For example, before the rotor can be removed for inspection, various exhaust system components, including for example such heat-insulating duct work like the cowl, the forward plenum wall and other components, first need to be disassembled and removed to allow access to the gas turbine rotor. Each component of the heat-insulating duct work of the exhaust system of a gas turbine engine defines an internal liner having an exposed surface for facing the hot exhaust gases that flow through the exhaust system during operation of the engine. Each such component defines an external shell that is spaced apart from and opposes the internal liner and is exposed to the ambient atmosphere. Each such component includes a heat resistant insulation that is disposed in the space between the internal liner and the external shell. The surface of the external shell that faces the ambient atmosphere is the so-called shielded surface.
Removal of these heat-insulating duct work components requires disassembly of the field joints that connect these exhaust system components to one another. Typical of the field joints that one finds connecting the exhaust system components are either those of the so-called hot flange design or those of the so-called cold flange design.
Exhaust systems employing the so-called hot flange design are provided with the capped/encapsulated insulation and require the site personnel to perform external work during the disassembly/reassembly of the components of the exhaust system. Such hot flange design causes the flange to be directly exposed to the hot exhaust gas, which typically attains temperatures of ranging from around 900 deg F. to 2,000 deg F. Due to the temperature difference between the high temperature exhaust gas within the exhaust system components and the far lower ambient temperature external to the exhaust system components, the thermal stresses on the flanges at the field joints between such components cause cracks and other heat-induced distortions in the flanges as well as fatigue in the bolts joining the flanges. Such degradations in the field joints reduce the useful life expectancy of the exhaust system components and pose potential safety hazards due to increased incidence of exhaust gas leaking through such degraded field joints.
Exhaust systems employing the so-called cold flange design are provided with internal insulation and a floating liner system that protects the flanges from being directly exposed to the high temperature exhaust gas flowing inside the components of the exhaust system. However, assembly and disassembly of the field joints of the exhaust system components employing this so-called cold flange exhaust system design with the internal liner system requires the site personnel to perform work both inside the exhaust system housing and outside of the exhaust system housing. Such work inside the exhaust system housing requires the erection of scaffolding inside the exhaust system housing. Such inside and outside work assignments significantly increase the required disassembly-reassembly time relative to exhaust systems employing the so-called hot flange design.